(1.1) Technical field
The present invention relates to fuzzy membership function circuits indispensable for constructing novel fuzzy control systems, and more particularly to fuzzy membership Z function circuits, fuzzy membership S function circuits, fuzzy logic circuits for use in composing other fuzzy membership function circuits based on these function circuits, programmable multi-membership function circuits thus composed for giving various membership function outputs in response to external control signals, etc.
(1.2) Limitation of digital computers and novel fuzzy logic circuits operable in current mode.
Fuzzy logic handles fuzziness, i.e. "vagueness." Human thought and behavior involve vagueness. If such vagueness can be expressed in terms of numbers or amounts or theorized, the system will find application to the design of community systems such as traffic control systems, emergency or applied therapeutic systems and the like and to the design of robots simulating the human being. Ever since the concept of fuzzy sets was proposed by L. A. Zadeh in 1965, research has been conducted on fuzzy logic as a means for handling "vagueness" from the above viewpoint. However, many research efforts are presently directed to the application of the logic to software systems for use with digital computers. The digital computer is adapted to perform operation based on binary logic using 0 and 1. Although the operation is processed very strictly, there is a need to use an A/D converter circuit for feeding analog quantities. The computer therefore has the problem of requiring a long period of time to obtain the final result by processing a vast quantity of information. Further the programs for the application of fuzzy logic are bound to become complex and require a large-sized digital computer for complicated processing, hence poor economy.
Since fuzzy logic handles continuous values (0, 1) in the section of from 0 to 1, the logic is inherently incompatible with digital computers which operate on binary logic. Further because fuzzy logic handles vague quantities having a range, the strictness required thereof is not as high as is required of digital computers. Accordingly, it is desired to provide novel circuits which are suitable for handling fuzzy logic.
To meet the demand, the present inventor has already proposed many fuzzy logic circuits which operate in current mode (as disclosed, for example, in U.S. patent application Ser. No. 714,809). The fuzzy logic circuits proposed by the present inventor include bounded difference circuits, complement circuits, bounded-sum circuits, bounded-product circuits, union (MAX) circuits, intersection (MIN) circuits, absolute-difference circuits, implication circuits, equivalence circuits, etc. All of these circuits operate in current mode. All the above fuzzy logic circuits have the feature that the circuit comprises the combination of one or a plurality of bounded-difference circuits and addition (subtraction) circuit. Since addition and subtraction in current mode can be realized merely by wiring (wired sum or wired subtraction), it can be said that a fuzzy bounded-difference circuit is basically the sole component unit of all the foregoing fuzzy logic circuits. It therefore follows that the fuzzy logic circuit operable in current mode has many advantages in respect of the design of the circuit and fabrication of the circuit as an IC.